Method of making glue from hides



UNITED STAT S Patented January 5, 1904.

PATENT OFFICE.

METHOD OF MAKING GLUE FROM HIDES.

SPECIFICATION forming part of Letters Patent No. 748,866, dated January 5, 1904.

Application filed March 3,1902. Serial No. 96,559. (No specimena) To all whom it may concern/. 7

Be it known that LEDWARD R. HEWITT, a citizen of the United States, and a resident of Garden City, in the county of Queens, State of New York, have invented certain new and useful Improvements in Methods of Making Glue from Hides, of which the following is a full and true description.

This invention relates to a novel process for manufacturing glue from animal hides; and the improvement consists,broadly,in subjecting the hides to treatment with two reagents which when combined in solution and precipitated will cause said reagents and all the impurities also in the solution to assume such form that they can all be readily separated mechanically to leave a clear solution.

In the manufacture of glue from hides or skins the latter are usually subjected to a process of liming for several months before they are boiled to dissolve the glue. One of the important advantages of the present invention is that the novel process can be carried out in less than a week.

There sometimes is produced from hides by any method a glue solution which can be filtered while in an acid state through an ordinary filter press; but when an alkaline earth is added to the solution to neutralize it, salts are formed with the impurities, which salts are either soluble or are held in suspension in a very fine state. If soluble, they crystallize in the glue when the solution is evaporated, jellied, and dried, and if solid in a fine state they will not be separated in the filter-press and will also remain in the glue. It is necessary to neutralize the glue solution, because an acid glue is not marketable, and aglue having crystalline impurities is equally objectionable,

In another application for patent, filed March 7,1902, Serial No. 97 ,133, I have described my process for manufacturing glue, which consists, broadly, in subjecting the raw stock to successive treatments in aqueous solutions formed with cold water and cold sulfurous-acid gas and then recovering the acid for repeated use from the solutions used for this purpose. That process works well to extract the calcium salts from bones, so'thatthe resulting soft bones can readily be dissolved to form the glue solution.

Such

I have found that if theglue solution from hide-stock be treated in accordance with the method above described for treating solutions obtained from bones the same results as to clarifying the solution will be obtained; but in making glue from such hide-stock it is necessary to properly prepare and hydrate the skins before they are dissolved in hot water, as above described. This preliminary treatment preferably includes the use ofacid, and I have devised an improved method whereby the hides can be prepared in a very short time, and a perfectly clear glue solution will result. In accordance with the present improvement the acid used for the preliminary treatment is the diluteform of the solution of sulfurous acid which has been used to extract the calcium salts from the bones. The extraction may be executed in any well-known way, and therefore'l do not describe in detail the method disclosed in my application for patent, Serial No. 97,138, filed March 7, 1902. This solution is placed on the hidesin sufficient quantity to cover them. Before this is done, however, in case the hides have been limed for preservation, they should be neutralized, as the subsequent reaction would otherwise generate too much heat, and it is necessary for the production of good glue that the temperature be kept down throughout the process. The acid solution used for treating the hides should preferably not have more than two per cent. of sulfurous acid and should be saturated with an amount of the lime salts from the bones which is equal to about two per cent. of its own volume. These proportions may, however, be varied without a departure from the invention. The solution should be applied cold on the hides that is, below Fahrenheit or below the temperature at which the glue will render, for rendering must be prevented until the preliminary treatment is completed. This preliminary treatment may be continued from three days to aweek, depending on the thickness of the hides and on the temperature of the reaction. During this time, as is indicated by the swelling of the hides, the glueyielding parts take up one or more molecules of the water of the acid solution, thus becoming partially hydrated, which shortens the time required afterward to dissolve the hides. During this treatment also the hides become impregnated with the phosphate and sulfite of calcium in the acid solution, and they become bleached thereby. After the hides have remained long enough in this solutionthat is, after they have become sufficiently hydrated or plumped, which is readily discerned by one skilled in the artthe solution is drawn oif, and the acid is recovered from it by treatment with open or live steam in a closed tank or vessel. By the steam treatment the phosphate and sulfite are separated from the solution, and the acid is recovered both as a free gas and in a pure solution. The free gas is cooled and put in solution in cold water to be used again to. extract the lime salts from bones, and the recovered acid in solution may be cooled and also used for the same purpose. Then these acid solutions, saturated with the lime salts of the bones, can be used after having first been diluted to treat the hide-stock in preparation for the gluedissolving operation, as above described. After the hides are thoroughly prepared for the dissolving operation they are washed one or two times to remove the excess of acid, which in too great amount will cause a de composition of the glue during the dissolving operation, although I have found it to be advantageous to have the stock slightly acid during such operation. The hides are next treated in water hot enough to dissolve them, but preferably well under the boiling-point in order not to injure the glue. The resulting glue solution contains both the calcium phosphate and the calcium sulfite and also some floating animal matter. If now this solution be neutralized by adding one of the alkaline earthssuch as calcium, barium, or strontium oxidsa granular precipitate of the salts will be formed, and the particles will be so large that they can readily be separated in an ordinary filter-press, so that the clear glue solution will flow therefrom. This precipitate also possesses the peculiar property of causing to become attached to it all the other impurities in the solution, which are either carried down in the solution or else prevented from passing through the filterpress, entirely by means of this precipitate. I believe that this result is due to the presence of both of the salts and that they combine and precipitate as a double salt when the neutralizing agent is added. The presence of both salts seems to cause the excess of acid in the glue to be put in combination, which acid would otherwise tend to prevent the formation of a precipitate of the large particles. The salts precipitate in the form of flaky crystals, which is the reason why I believe they combine to form a double salt. During the particular operation of preparing the hides I have tried a sulfurous-acid solution alone; but the subsequent neutralization of the glue solution resulted only in the formation of a precipitate which is too fine to be mechanically separated. When phosphoric acid alone is used to prepare the hides and the glue solution therefrom is neutralized by the addition of lime or monobasic phosphate of lime, the resulting precipitate is gelatinous and almost impossible to separate mechanically; but when the phosphate and sulfite are both employed, as in the sulfurous-acid solution which has been used on bones, the result of neutralizing the glue solution is a large granular precipitate, which is very readily separated, as described, in an ordinary filter-press and carries with it all the other impurities in the solution.

As stated above, the acid solution used on the bones can be put directly into the glue solution obtained from the hide-stock; but the stock in that case is first prepared by treatment in a pure aqueous solution of sulfurous acid, thereby partially hydrating the stock.

The great advantage possessed by the method above described of preparing the hides themselves with the acid solution which has been used on the bones is that such a solution is practically a waste product and does not require special preparation, which would be a great additional expense. Also after the use of the solution on the hides the acid can be recovered by treatment with open steam in a closed tank in the same way that the acid is recovered when the solution is used only on the bones. Furthermore, only one application of a solution is necessary in the case when the solution first used on the bones is applied to the hides instead of to the glue solution obtained from the hides. Since the water must be evaporated from the glue solution, it is obviously an advantage to apply the used bone-extracting solution to the hides themselves, thereby avoiding increasing the amount of water of the glue solution.

In some cases when the hides are prepared with the bone-extracting solution they may not retain a sufficient amount of the calcium salts, so that when the glue solution is neutralized the desired precipitate will not be obtained. In such case a small amount of the bone-extracting solution may be added to the neutral glue solution, thereby making it acid again and increasing the amount of lime salts in it. When the glue solution, which is now acid, is again neutralized, the desired precipitate will undoubtedly be obtained; but if not this method may be continued until it is obtained;

Having described my invention, what I claim is l. The improvement in the art of making glue from hides, which consists in preparing the hides in a cool aqueous solution of sulfurous acid which contains calcium phosphate and calcium sulfite; then dissolving the hides; and finally adding a neutralizing agent to precipitate the two salts and clarify the glue solution.

2. The improvement in the art of making glue from hides, which consists in treating the hides with an aqueous solution of sulfurous'acid which contains calcium phosphate and calcium sulfite.

3. The improvement in the art of making glue from hides, which consists in treating the hides with a solution of two acid salts, dissolving the treated hides in hot water, and neutralizing the resulting solution; said salts being of such character that when the solution is neutralized a precipitate of the salts is formed, which possesses the peculiar property of causing to become attached to it all the other impurities in the solution, all in a form readily separable, mechanically, from the solution.

4. The improvement in the art of making glue from hides, which consists in preparing the hides in a. cool aqueous solution of sulfurous acid which contains calcium phosphate and calcium sulfite, then dissolving the hides, neutralizing the glue solution, adding to the glue solution a little of the solution of sulfurous acid containing phosphate and sulfite of calcium, and finally again neutralizing.

5. The improvement in the art of making glue from hides, which consists in subjecting the hides to treatment with a solution of sulfurous acid and the calcium salts of bones, dissolving the hides, and'neutralizing the resulting glue solution.

6. The improvement in the art of making glue from limed hides, which consists in first neutralizing the hides, hydrating the hides by means of an aqueous solution of sulfurous acid'whioh contains calcium phosphate and calcium sulfire, dissolving the hides, and finallyadding a neutralizing agent to the glue solution, to precipitate the two salts and impurities in readily separable form.

7. The improvement in the art of making glue from hides, which consists in hydrating the hides by means of an aqueous solution of sulfurous acid, which contains calcium phosphate and calcium sulfite, and then washing the hides to remove the excess of acid, dissolving the hides in hot water, and then neutralizing the solution.

In witness whereof I have hereunto signed my name this 21st day of February, 1902.

EDWARD R. HEWITT. In presence of-- W. H. BERRIGAN, JAMES J Oosenovn. 

